Hereditary means passed down from parents to children through biological inheritance. When something is hereditary, it transfers through your genes, the microscopic instructions in your cells that determine traits like your eye color, hair texture, and blood type.

Some hereditary traits are obvious and harmless: if both your parents have brown eyes, you probably inherited brown eyes too. Other hereditary conditions are more serious. Sickle cell disease is a hereditary blood disorder that runs in families. If scientists discover that a certain type of cancer is hereditary in someone's family, relatives know they might need extra medical screening.

In some countries, royal titles and positions were hereditary: a king's son became king, a duchess's daughter became duchess, regardless of ability or merit. This hereditary system of power lasted for centuries in Europe and elsewhere.

You'll sometimes see hereditary confused with heredity (the process of passing traits) or congenital (present from birth but not necessarily inherited). Something hereditary specifically comes from your ancestors through genes, traveling through generations of your family tree.